Field of the Invention
This invention relates to a DC to DC converter assembly, and in particular a DC to DC converter assembly for connecting first and second high voltage DC power transmission networks.
Description of Related Art
With the increasing prevalence of renewable energy generators, such as off-shore wind, there is a growing need to transmit direct current (DC) electrical power from one high voltage DC power transmission network to another high voltage DC power transmission network.
At present the only manner in which such transmission between high voltage DC networks can be achieved is through the provision of first and second conventional voltage converters 10, 12 which are interconnected by a high power transformer 14, as shown in FIG. 1. The first voltage converter 10 converts an incoming DC voltage from a first voltage DC network 16 into an alternating voltage which the transformer 14 increases or decreases to allow conversion by the second voltage converter 12 to a desired outgoing DC voltage, as required in a second voltage DC network 18.
High power transformers typically operate at 50 or 60 Hz while the size and weight of the components forming the first and second voltage converters 10, 12 and the power transformers themselves can be dramatically reduced by operating the converters 10,12 at a much higher frequency, typically in the region of 500 Hz. As a result the aforementioned scheme operating at 50 or 60 Hz requires a very large and heavy transformer and other passive energy storage elements which are often unsuitable for installation in a required location.
In addition, high power high frequency (i.e. circa 500 Hz) transformers are costly, bespoke components which are not currently available on a commercial scale.
There is, therefore, a need for an improved means of connecting first and second high voltage DC power transmission networks which obviates the need for a large, heavy and costly high power transformer.